Impact of pharmacokinetics (PK) of sunitinib (SU) and its metabolite SU12662 on clinical outcome and toxicity in metastatic renal cell cancer (mRCC) patients.

Abstract

506 Background: Pharmacological activity of SU is usually attributed to SU and its active metabolite SU12662, known to exhibit similar potency in inhibiting tyrosine kinase activity and cellular proliferation in vitro. However, equivalence is not clearly demonstrated towards clinical endpoints. The objective of this phase 2 study was to determine the impact of SU and SU12662 on clinical outcomes and toxicity in mRCC patients (NCT00943839). Methods: Patients with mRCC, eligible for SU in the first line setting, were prospectively included. SU was given orally at 50 mg qd for 4 weeks on/2 weeks off until progression or unacceptable toxicity. Minimal concentration at steady-state (CSSmin) was evaluated by high-performance liquid chromatography at day 28 of each cycle for both SU and SU12662. Data for tumor response, survival, and toxicity were recorded. Kaplan-Meyer’s curves with log-rank tests and cox regression models were used to identify relationships between PK parameters and survival. Chi2 tests and student t-tests were used to identify relationships with toxicity. Results: 41 patients in 7 French centers were included between 2009 and 2012. 16 patients had favourable prognosis, 13 intermediate prognosis, and 1 poor prognosis according to IMDC risk groups (Heng, J Clin Oncol 2009). Median follow-up was 30.6 months. Median progression-free survival (PFS) was 20.2 months and median overall survival (OS) was 39.5 months. Mean CSSmin for SU and SU12662 were 57.2 and 29.8 ng/ml, respectively. CSSmin of SU12662 was independently correlated to poor PFS and OS (p = 0.01 and 0.003 respectively). Patients with a mean CSSmin of SU12662 higher than 42.5 ng/ml had a worse PFS and OS compared to patients with lower concentrations: 5.7 months and 5.7 months versus 20.6 months and 39.5 months (p = 0.01 and 0.002 respectively). High CSSmin of both SU and SU12662 were associated with increased incidence of asthenia (p<0.001). Conclusions: High exposure to SU12662 was associated with poor outcomes and increased asthenia for patients with mRCC treated with SU in the first line setting. It may be related to a higher metabolism and unequal activity between SU and SU12662 in vivo. Clinical trial information: NCT00943839.